It is known that there are various methods of building three-dimension (3D) objects, including additive manufacturing (AM), subtractive manufacturing (SM) and injection molding (IM). Additive manufacturing (AM), in particular, concerns technologies that synthesize 3D objects by selectively depositing or adding layer-upon-layer of material, whether the material is plastic, metal, concrete or polymer. Different processes of additive manufacturing are, for example, extrusion (e.g., fused deposition modeling, fused filament fabrication), light polymerization (e.g., stereolithography, digital light processing), lamination (e.g., laminated object manufacturing), powder bed (e.g., electron beam melting, selective laser melting, selective heat sintering, selective laser sintering), powder fed (e.g., direct energy deposition), and electron beam fabrication.
A common problem with conventional AM machines and processes involves the uncertainty surrounding the integrity and solidity of each layer formed during the build process. Another problem concerns the integrity and strength in the bonding between neighboring layers of material, i.e., lack of fusion. Other physical defects that are typical in AM processes include porosity, fatigue cracks initiating at pores close to surfaces of the AM part, and surface roughness which has been known to affect fatigue life of the AM part.
A known approach for determining the manufacturing quality of an AM part consists of destructively evaluating a significant number of parts and looking for common defects. However, this approach is costly and time consuming, and negates the benefits of the AM process, such as being able to quickly and cost-effectively produce new and different parts.
There are also nondestructive testing techniques to detect defects in an AM part after the build process has finished. For example, one type of nondestructive testing involves a person holding a handheld instrument adapted for detecting defects in the completed AM part and scanning sections of the AM part for analysis. However, these techniques suffer from drawbacks including the fact that they are not real-time, in-situ processes and thus lack the ability to detect and fix the defects at the time they are created. The defects become inherent in the AM part by the time the entire build process is completed, thereby making it impossible to correct the defects. As a result, the entire AM part must be discarded and a new part made. Such an outcome entails excessive material waste and is costly.
Further, the person may fail to hold the detection instrument steady and scan the AM part along straight paths which are necessary to accurately determine the exact location of defects in the AM part. Thus, imprecise detection of defects may occur. In addition, complex geometries of AM parts also pose a challenge for post-completion nondestructive testing techniques. Many parts made by AM have internal structure that are inaccessible by less geometry-sensitive techniques, such as penetrant testing and magnetic particle testing.